Centos7のdocker imageでsystemdが使えるものを調査した

## About
centos7のdocker imageにはfakesystemdが導入されているという問題があり使用を控えていましたが、風の噂でsystemdが使えるようになったので調査しました。

* 更新のdocker hubはここ　[centos Repository | Docker Hub Registry - Repositories of Docker Images](https://registry.hub.docker.com/_/centos/tags/manage/)


## centos:latest& centos:7 & centos:centos7（7322fbe74aa5）
* systemdがインストールされている

```
[root@f9681438b272 /]# cat etc/redhat-release
CentOS Linux release 7.1.1503 (Core)
[root@f9681438b272 /]# cat /etc/centos-release
CentOS Linux release 7.1.1503 (Core)
[root@f9681438b272 /]# which systemctl
/usr/bin/systemctl
[root@f9681438b272 /]# yum list | grep systemd
systemd-container.x86_64                 208.20-6.el7.centos             @systemdcontainer
systemd-container-libs.x86_64            208.20-6.el7.centos             @systemdcontainer
golang-github-coreos-go-systemd-devel.noarch
systemd.x86_64                           208-20.el7_1.5                  updates
systemd-devel.i686                       208-20.el7_1.5                  updates
systemd-devel.x86_64                     208-20.el7_1.5                  updates
systemd-journal-gateway.x86_64           208-20.el7_1.5                  updates
systemd-libs.i686                        208-20.el7_1.5                  updates
systemd-libs.x86_64                      208-20.el7_1.5                  updates
systemd-python.x86_64                    208-20.el7_1.5                  updates
systemd-sysv.x86_64                      208-20.el7_1.5                  updates
```

## centos:7.0.1406 & centos:7.0.1406（feb2761601e7）
* systemdがインストールされていない(fakesystemd)

```
[root@842b3d42833f /]# cat /etc/redhat-release
CentOS Linux release 7.0.1406 (Core)
[root@842b3d42833f /]# cat /etc/centos-release
CentOS Linux release 7.0.1406 (Core)
[root@842b3d42833f /]# which systemctl
/usr/bin/which: no systemctl in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
[root@842b3d42833f /]# yum list | grep systemd
fakesystemd.noarch                       1-17.el7.centos                 @fakesystemd/$releasever
systemd-libs.x86_64                      208-11.el7                      @CentOS/$releasever
golang-github-coreos-go-systemd-devel.noarch
systemd.x86_64                           208-20.el7_1.5                  updates
systemd-devel.i686                       208-20.el7_1.5                  updates
systemd-devel.x86_64                     208-20.el7_1.5                  updates
systemd-journal-gateway.x86_64           208-20.el7_1.5                  updates
systemd-libs.i686                        208-20.el7_1.5                  updates
systemd-libs.x86_64                      208-20.el7_1.5                  updates
systemd-python.x86_64                    208-20.el7_1.5                  updates
systemd-sysv.x86_64                      208-20.el7_1.5                  updates
```

## centos:7.1.1503 & centos:centos7.1.1503
* systemdがインストールされていない(fakesystemd)

```
[root@7cd70b31a95f /]# cat /etc/redhat-release
Derived from Red Hat Enterprise Linux 7.1 (Source)
[root@7cd70b31a95f /]# cat /etc/centos-release
CentOS Linux release 7.1.1503 (Core)
[root@7cd70b31a95f /]# which systemctl
/usr/bin/which: no systemctl in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
[root@7cd70b31a95f /]# which systemctl
/usr/bin/which: no systemctl in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
[root@7cd70b31a95f /]# which systemctl
/usr/bin/which: no systemctl in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin)
[root@7cd70b31a95f /]# yum list | grep systemd
fakesystemd.noarch                       1-17.el7.centos                 @fakesystemd/$releasever
systemd-libs.x86_64                      208-20.el7                      @CentOS/$releasever
golang-github-coreos-go-systemd-devel.noarch
systemd.x86_64                           208-20.el7_1.5                  updates
systemd-devel.i686                       208-20.el7_1.5                  updates
systemd-devel.x86_64                     208-20.el7_1.5                  updates
systemd-journal-gateway.x86_64           208-20.el7_1.5                  updates
systemd-libs.i686                        208-20.el7_1.5                  updates
systemd-libs.x86_64                      208-20.el7_1.5                  updates
systemd-python.x86_64                    208-20.el7_1.5                  updates
systemd-sysv.x86_64                      208-20.el7_1.5                  updates
```

## まとめ
dockerのimageは同じタグでも定期的に更新されているらしいので、ハッシュ値を見て判断した方がよさそうです。というかなぜfakesystemdは辞めたのか理由が知りたい。